单例

配置文件

IP = '1.1.1.1'
PORT = '3306'



单例1.py

# 单例模式  （省内存）
#     基于某种方法实例化多次得到的实例是同一个
# 为何用单例模式
#     当实例化多次得到的对象中存取的属性都一样的情况下，应该将多个对象指向同一个内存，即同一个实例

# 如何用：
# 实现单例方式一

import settings


class Mysql():
    __isinstance = None

    def __init__(self,ip,port):
        self.ip = ip
        self.port = port

    @classmethod
    def from_conf(cls):
        if cls.__isinstance is None:
            cls.__isinstance = cls(settings.IP,settings.PORT)

        return cls.__isinstance

obj1 = Mysql.from_conf()
obj2 = Mysql.from_conf()
obj3 = Mysql.from_conf()

print(obj1)
print(obj2)
print(obj3)

# <__main__.Mysql object at 0x1033a57f0>
# <__main__.Mysql object at 0x1033a5ac8>
# <__main__.Mysql object at 0x1033a5b70>


# 仅适用于对象中存的东西一样

# <__main__.Mysql object at 0x1033a57b8>
# <__main__.Mysql object at 0x1033a57b8>
# <__main__.Mysql object at 0x1033a57b8>

# 不一样的单独造
obj4 = Mysql('2.2.2.2',3309)
print(obj4)




单例2装饰器.py

# 实现单例方式二
import settings
# 如果是从配置文件里面获取配置的话

# 装饰器

def singleton(cls):   #func传被装饰的函数，类
    _instance = cls(settings.IP,settings.PORT)   #放到类里面变成类属性  cls.__instance
    def wrapper(*args,**kwargs):
        if not args and not kwargs:
            return _instance
        return cls(*args,**kwargs)

    return wrapper


@singleton
class Mysql():
    def __init__(self,ip,port):
        self.ip = ip
        self.port = port

obj1 = Mysql()
obj2 = Mysql()
obj3 = Mysql()
print(obj1 is obj2 is obj3)
obj4 = Mysql('2.2.2.2',3309)
print(obj1)
print(obj2)
print(obj3)
print(obj4)

# # 运行过程，遇到@语法就会将装饰器正下方的那个名字当做参数传进来，然后将返回的结果重新赋值给这个名字：
# @singleton          #Mysql = singleton(Mysql)
# class Mysql():
#     def __init__(self, ip, port):
#         self.ip = ip
#         self.port = port
#
#
#
# # singleton调用发生了
# def singleton(cls):   #cls = Mysql                 @singleton   #Mysql = singleton(Mysql)    Mysal = wrapper
#     def wrapper(*args,**kwargs):
#         res = cls(*args,**kwargs)
#         return res
#     return wrapper


# obj = Mysql('1.1.1.1',3306)
# print(obj.__dict__)



单例3元类.py

# 实现单例方式三
import settings




class Mymeta(type):
    def __init__(self,class_name, class_bases, class_dic):   #在Mysql造出来之前发生的   self = Mysql
        super(Mymeta, self).__init__(class_name, class_bases, class_dic)
        obj = self.__new__(self)               #造出一个Mysql的对象
        self.__init__(obj,settings.IP,settings.PORT)    #从配置文件中加载配置完成Mysql对象的初始化
        # 保存下来
        self.__instance = obj

        # print(self.__instance)
        # print(self.__instance.__dict__)




    def __call__(self, *args, **kwargs):
        if len(args) == 0 and len(kwargs) == 0:
            return self.__instance

        obj = self.__new__(self)
        self.__init__(obj,*args,**kwargs)
        return obj









class Mysql(object,metaclass=Mymeta):
    def __init__(self,ip,port):
        self.ip = ip
        self.port = port



# Mysql()


obj1 = Mysql()
obj2 = Mysql()
obj3 = Mysql()
obj4 = Mysql('2.2.2.2',3309)